Overhaul of Resources (#125)

* Supporting resource templates with read resource callback

Fixes #123

* Aligning the resource data structures with the 2024-11-05 schema

- Introducing separate classes for Text and Blob ResourceContents
- Custom JSON converter to allow those types to be returned, making it easier to follow the type system against the spec
- Updated tests

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: Peder Holdgaard Pedersen <127606677+PederHP@users.noreply.github.com>

* Putting files back where they belong

* Adding an internal constructor to prevent overloads

* Addressing feedback

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>

* Update src/ModelContextProtocol/Protocol/Types/ResourceContents.cs

* Addressing feedback

---------

Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: Peder Holdgaard Pedersen <127606677+PederHP@users.noreply.github.com>

tests/ModelContextProtocol.Tests/ClientIntegrationTests.cs

@@ -224,7 +224,9 @@ public class ClientIntegrationTests : LoggedTest, IClassFixture<ClientIntegratio
 
         Assert.NotNull(result);
         Assert.Single(result.Contents);
-        Assert.NotNull(result.Contents[0].Text);
+
+        TextResourceContents textResource = Assert.IsType<TextResourceContents>(result.Contents[0]);
+        Assert.NotNull(textResource.Text);
     }
 
     [Theory]
@@ -241,7 +243,9 @@ public class ClientIntegrationTests : LoggedTest, IClassFixture<ClientIntegratio
 
         Assert.NotNull(result);
         Assert.Single(result.Contents);
-        Assert.NotNull(result.Contents[0].Blob);
+
+        BlobResourceContents blobResource = Assert.IsType<BlobResourceContents>(result.Contents[0]);
+        Assert.NotNull(blobResource.Blob);
     }
 
     // Not supported by "everything" server version on npx